Beyond the data: controlling CO2 with Purrmetrix

This is cool: the team at LCMB have been using Purrmetrix to go beyond data gathering and get into some home brewed building control.

LCMB have been monitoring the environment in a university facility for several months using Purrmetrix CO2 and temperature sensors to look at the relationship between comfort and productivity. One space in particular caught the attention of LCMB and the university estates team: an office area which had obvious ventilation problems. With a lot of people using the space the building systems were struggling to keep up with the ventilation needed, especially in winter, when opening windows was unattractive.

It was commonplace to see CO2 levels rising above 1500 ppm, a level where concentration and decision making becomes impaired.

KCL CO2

But rather than going for a costly building services overhaul, the LCMB team decided to go one better and implement their own fix, using ducted fans and a Raspberry Pi to keep the CO2 in the office within controlled limits.

Two fans were set up to provide good coverage across the whole space; each had their own Raspberry Pi low cost computer to read the data from API on the Purrmetrix web service and to drive the fans using a digital to analogue converter. The fans were ducted from outside so the set up also needed a heater in front of the air to temper it to the right temperature. This might not be the prettiest set up, but it’s a prototype and a big improvement on a CO2 headache.

KCL fan

The project took a few days of tinkering time to connect the hardware, in particular setting up the Pi and configuring the internet access for it from the university network. But once the hardware was connected and the right scripts were implemented it produced an immediate result.

KCL CO2 controlled

There had been some concerns about noise levels and air movement – in practice the team found that to keep levels of CO2 around 700 ppm (+/- 100 ppm) the fan was operating at 50 – 60% for much of the day. This delivered a good trade off between air quality and noise level. Allowing a higher CO2 level (around 1000 – 1200 ppm, which is considered acceptable) fans could be quieter, cycling on/off most of the day. In warmer weather as windows are opened, the fans are working much less frequently.

‘Once we had the data from Purrmetrix it was irresistible to have a go at creating a solution.’ explains Tom Cudmore, senior consultant at LCMB, ‘We considered using the alerts system within Purrmetrix to create a HTTP call that would activate the fan, but in the end we decided to keep the alerts for exceptions and take the data direct from the API every two minutes. It took a few weeks to source the right fan product and write the scripts, but we think the results speak for themselves – we’d be happy to work in this environment now.’

If you have a problem office and would like to re-create this low cost solution, to trial the impact in your workplaces, here are the components you will need:

– Fan (we used Helios RR-EC in-line duct fan) sized according to the room volume and desired conditions
– Ducting and window blanking plate
– Heater to put in front of the fan and temper the outside air
– Power supply for fan and heater
– Wiring from analogue convertor to fan
– Digital to analogue convertor – we used a LucidControl device
– Raspberry Pi with internet access and configured for remote access
– Purrmetrix kit – in this case with CO2 sensor

And if you want a copy of the script that LCMB developed, just get in touch.

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